Method of manufacturing a magnetic head

ABSTRACT

A magnetic head comprising first and second magnetic core halves held in abutment against each other and a gap-defining spacer interposed therebetween, and having an elongated tape-contact surface extending across said gap-defining spacer. The gap-defining spacer has the same crystal structure as that of said first and second core halves and is made of a non-magnetic material including the same principal component as those of said first and second cores halves. The gap-defining spacer is welded to said first and second core halves in accordance with a solid-phase welding method based on a solid-phase reaction.

This application is a continuation of application Ser. No. 802,952,filed Nov. 27, 1985, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to a magnetic head formagnetically recording and reproducing signals on and/or from a magneticrecording medium such as magnetic tape and a method for making such amagnetic head, wherein non-magnetic zinc ferrite is used as agap-defining spacer material.

Various types of magnetic heads have been developed. Of these, amagnetic head in which glass bodies are used for defining a magnetic gapthereof is general which further includes first and second magnetic corehalves each being made of, for example, Mn-Zn single crystal ferrite.The first and second magnetic core halves are held in abutment againsteach other so as to form the magnetic gap. The magnetic gap is occupiedby a gap-defining spacer material such as SiO₂ so that it is sandwichedbetween the first and second core halves and the gap-defining spacer iswelded to them by means of the glass-welding method.

However, according to the glass-welding method, the welding is performedusing glass melted by heating to a temperature of about 700° C., withthe results that the glass and SiO₂ diffuse and penetrate into theferrite cores on the welding process. The diffusion and penetrationresult in a substantial increase in gap-length, worsening magnetic headperformance, and further the difference of coefficient of thermalexpansion therebetween sometimes causes breakage of the magnetic headand deterioration of magnetic permeability.

On the other hand, Japanese Patent Provisional Publication No. 58-185437discloses a magnetic head wherein non-magnetic zinc ferrite is employedas a gap-defining spacer material. This magnetic head not onlyeliminates the above-noted problems but also provides various advantagess including increase in workability. However, the prior art magnetichead has a structure in which the gap-defining spacer is interposedbetween the magnetic core halves and bonded thereto by a bondingmaterial. One of problem with such a head structure is that there aredifferences in physical properties between the bonding material and themagnetic core halves or gap-defining spacer, thus resulting in theoccurrence of strain between the spacer and magnetic cores anddeterioration of magnetic characteristics. Furthermore, dispersion inwear resistance of the tape-contact surface thereof occurs at the jointportions between the gap-defining spacer and magnetic cores, therebyshortening the usable life time of the magnetic head because of apartial wear. Therefore, a further improvement will be required from aviewpoint of increase in durability of the magnetic head, preventing themagnetic characteristics from being deteriorated, and increase inrunning properties of the magnetic head.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a newand improved magnetic head which overcomes the above-describeddisadvantages inherent in the prior art magnetic heads.

It is a further object of the present invention to provide a method ofproducing such a magnetic head.

A feature of the present invention is that a gap-defining spacerinterposed between first and second magnetic core halves has the samecrystal structure as that of the first and second magnetic core halvesand is made of a non-magnetic material including the same principalcomponent as that of the magnetic core halves.

A further feature of the present invention is that the bonding betweenthe gap-defining spacer and magnetic core halves is not performed usingan adhesive material but is effected in accordance with the solid-phasewelding method in which the weld is consummated by pressure or by heatand pressure without fusion on the basis of solid phase reaction.

These features of this invention provide advantages in that the weldingsurfaces of the gap-defining spacer are integrally welded to those ofthe magnetic core halves so that there is no apparent joint between thespacer and cores, and mechanical properties of the magnetic head aresubstantially equalized and thus dispersion of wear resistant propertieson the tape-contact surface thereof is eliminated, with improveddurability and running properties of the head and with no preventeddeterioration of magnetic properties caused by strain between the spacerand magnetic cores.

A method of fabricating a magnetic head of the present inventioncomprises the steps of providing first and second blocks of a magneticmaterial, each of the blocks having a mirror-finished surface, forming aslot in said mirror-finished surface of the first block in alongitudinal direction thereof, forming recesses in an upper side ofsaid surface of the first block in a transverse direction from said slotto one end thereof, and forming recesses in the mirror-finished surfaceof the second block so as to be equal to those of the first block inshape and position. Thereafter, a gap-defining layer is provided on saidupper side of the surface of the first block and further a magneticlayer, having a thickness equal to a thickness of the gap-defininglayer, is provided on a lower side of the surface of the first block.The first and second blocks are joined together by faying the layers ofthe first block to the mirror-finished surface so that said recessesthereof face each other, and a solid-phase welding is then performedwith respect to the fayed surfaces so that the first and second blocksare integrally welded to form a welded block. The welded block is cutalong lines provided so as to cross the recesses and slot.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and features of the present invention will become morereadily apparent from the following detailed description of thepreferred embodiment taken in conjunction with the accompaying drawingsin which:

FIG. 1 is a perspective view of a magnetic head completed in accordancewith the present invention; and

FIGS. 2a through 2d are illustrations of the steps of fabricating amagnetic head according to the present invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is illustrated a magnetic head accordingto the present invention. The magnetic head comprises a first magneticcore half 11a and a second magnetic core half 11b held in abutment witheach other and a gap-defining spacer 12 interposed therebetween, and hasan elongated tape-contact surface 14 formed thereby. The first magneticcore half 11a is U-shaped to form a coil winding slot 13. Each of themagnetic core halves 11a and 11b respectively has recesses 15 at theside of the tape-contact surface 14, recesses 15 being positioned at theboth ends of the gap-defining spacer 12 exposed on the tape-contactsurface 14 so as to define the gap width of gap of the head.

The first and second core halves 11a and 11b are each made of a magneticoxide material with spinel structure, whose principal component is ironoxide. For example, the core halves 11a and 11b are made of Mn-Zn singlecrystal ferrite consisting substantially of MnO (25 to 34 molar %), ZnO(14 to 19 molar %) and Fe₂ O₃ (52 to 56 molar %). The gap-definingspacer 12 is made of non-magnetic Zn (or Cd) single crystal ferritematerial with spinel structure which has the same principal component asthat of the magnetic oxide material. The non-magnetic Zn (or Cd) singlecrystal ferrite material consists of Fe₂ O₃ and Zn (or CdO) at a molarratio of 52 to 56:48 to 44 (99 wt %), CaO (0.5 wt %), and A1₂ O₃ (0.5 wt%).

That is, the gap-defining spacer 12 is made of a non-magnetic oxidematerial having the same crystal structure as that of the magnetic corehalves 11a and 11b and comprising the same principal component as thatof the magnetic cores. For example, ZnFe₂ O₄ is employed as theprincipal component, and CaO not more than 0.5 wt % and A1₂ O₃ of 0.5 to2 wt % are added thereto. In this case, it is also appropriate to useMgO or a combination of CaO and MgO not more than 0.5 wt % in totalamount in place of CaO.

The gap-defining spacer 12, as described above, is in sandwichingrelation to the magnetic core halves 11a and 111b and both is integrallywelded in accordance with the solid phase welding method on the basis ofthe solid phase reaction. A volume ratio of the gap-defining spacer 12and the magnetic core half 11a or 11b is 1:infinity, and therefore bothare integrally completely welded on the basis of the fact that thecrystal structure of the spacer 12 is equalized in a direction of thecrystal structure of the core whose volume is larger. As reported bySeiya Ogawa in "JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, vol. 23, No. 2August, 1967", diffusion scarcely occurs in the solid phase reaction.Therefore, it will be seen from the report that diffusion from thespacer 12 to the cores 11a, 11b scarcely occurs in the soild-phasewelding process. Even if the diffusion occurs, since the gap spacer 12is of the same crystal structure as those of the magnetic core halves11a and 11b, the gap-length scarcely varies due to the solid phasewelding. Furthermore, CaO, MgO or Al₂ O₃ contained in the gap spacermaterial serves to prevent the diffusion and penetration.

FIGS. 2a through 2d show a sequence of steps of fabricating a magnetichead according to the present invention. As illustrated in FIG. 2a, afirst elongated block 20a made of a Mn-Zn ferrite magnetic material isprovided which has a mirror-finished surface. The block 20a is machinedsuch that a winding slot 21 is formed in the mirror-finished surface ina longitudinal direction thereof and recesses 22a or controlling a trackwidth are formed in a transverse direction from the winding slot 21 toone end thereof. Furthermore, another block 20b, as shown in FIG. 2b,made of the same material as that of the block 20a and having the sameshape as that of the block 20a are prepared. to the recesses 22a inshape and position. A gap-defining spacer layer 23 made of anon-magnetic oxide material consisting of ZnFe₂ O₄, MgO and Al₂ O₃ at aweight ratio of 99:0.5:0.5 is deposited by the sputtering method on theflat portions 22c of the upper side of the block 20a as shown in FIG.2c. Here, the flat portions 22c are areas other than the recesses 22a onthe upper side surface of the block 20a. The thickness of the spacerlayer 23 deposited defines a gap length of the magnetic head. On theother hand, a thin layer 24 comprising the same magnetic material asthose of the first and second blocks is provided by the sputteringmethod on the lower side surface of the block 20a facing through thewinding slot 21 to the flat portions.

Thereafter, 30 to 40% of concentrated phosphoric acid liquid is appliedto the layers 23, 24 of the first block 20a and to the mirror-finishedsurface of the second block 20b, and then the blocks 20a and 20b arejoined together by faying the layers of the first block 20a to thesurface of second block 20b so that the recesses 22a and 22b of theblocks 20a and 20b confront each other. The joined blocks 20a and 20bare welded by means of the solid-phase welding on the basis of thesolid-phase reaction, thus forming a block 25 as shown in FIG. 2d. Thesolid-phase welding is achieved by keeping the fayed blocks 20a and 20bat a temperature between about 1250° C. and 1350° C. for about one hourin a nitrogen atmosphere having an oxygen partial pressure (5 molar %)in equilibrium with the content of oxygen in the Mn-Zn ferrite.

The block 25 is cut along dot-and-dash lines indicated in FIG. 2d acrossthe recesses 22a and 22b and the joint between the blocks 20a and 20b,thereby providing magnetic head blanks. Each of the magnetic head blanksis grounded to form a magnetic head as shown in FIG. 1.

It should be understood that the forgoing relates to only a preferredembodiment of the invention, and that it is intended to cover allchanges and modifications of the embodiment of the invention herein usedfor the purpose of the disclosure, which do not constitute departuresfrom the spirit and the scope of the invention. For example, although inthe foregoing description a Mn-Zn single crystal ferrite magneticmaterial is used as the material for making the block 20a and 20b, it isalso possible to use a polycrystal ferrite magnetic material for theblock 20a and/or the block 20b.

What is claimed is:
 1. A method of fabricating a magnetic head,comprising the steps of:providing first and second blocks made of singlecrystal ferrite, each of said blocks having a mirror-finished surface;providing a gap-defining spacer on an upper side of said surface of saidfirst block, said gap-defining spacer being made of a non-magneticferrite and having substantially the same crystal structure as that ofsaid first and second blocks and substantially comprising the samecomponent as that of said first and second blocks; faying said surfacesof said first and second blocks with said gap-defining spacer beinginterposed therebetween; and performing a solid-phase welding withrespect to the fayed surfaces so that said first and second blocks areintegrally welded and said non-magnetic ferrite of said gap-definingspacer is monocrystallized, the solid-phase welding being effected bykeeping said first and second blocks at a temperature between about1250° C. and 1350° C. for about one hour in an atmosphere having anoxygen partial pressure in equilibrium with the content of oxygen in thesingle crystal ferrite.
 2. A method of fabricating a magnetic head,comprising the steps of:providing first and second blocks made of singlecrystal ferrite, each of said blocks having a mirror-finished surface;forming a slot in said mirror-finished surface of said first block in alongitudinal direction thereof; forming a recess in an upper side ofsaid surface of said first block in a transverse direction from saidslot to one end thereof; forming a recess in said mirror-finishedsurface of said second block so as to be equal to those of said firstblock in shape and position; providing a gap-defining layer on the upperside of said surface of said first block, said gap-defining layer beingmade of a non-magnetic ferrite and having substantially the same crystalstructure as that of said first and second blocks and substantiallycomprising the same component as that of said first and second blocks;providing a magnetic layer, having a thickness equal to a thickness ofsaid gap-defining layer, on a lower side of said surface of said firstblock; faying said surfaces of said first and second blocks so that saidrecesses thereof face each other; performing a solid-phase welding withrespect to the fayed surfaces so that said first and second blocks areintegrally welded to form a welded block with said non-magnetic ferriteof said gap-defining layer being monocrystallized, the solid-phasewelding being effected by keeping said welded block at a temperaturebetween 1250° C. and 1350° C. for about one hour in an atmosphere havingan oxygen partial pressure in equilibrium with the content of oxygen inthe single crystal ferrite; and cutting said welded block along linesprovided so as to cross said recesses and said slot.
 3. A method asclaimed in claim 1, further comprising a step of applying a concentratedphosphoric acid liquid on said layers of said first block and saidmirror-finished surface of second block.
 4. A method as claimed in claim1, wherein said solid-phase welding is performed in a nitrogenatmosphere.
 5. A method as claimed in claim 2, wherein said solid-phasewelding is performed in a nitrogen atmosphere.